Searches for boosted low mass resonances decaying to $b$-quarks with the ATLAS detector

A search for new resonances decaying into a pair of bottom quarks in the boosted regime is reported using an integrated luminosity of $80.5~\mathrm{fb}^{-1}$ of proton-proton collisions at $\sqrt{s}=13~\mathrm{TeV}$ recorded by the ATLAS detector at the Large Hadron Collider. For the resonance to be boosted, an extra jet with high transverse momentum is required. The mass range $70$ and $230~\mathrm{GeV}$ is inspected. For the Standard Model Higgs boson, the observed signal strength is $\mu_{H} = 5.8 \pm 3.6~\text{(exp.)}~\pm 1.3~\text{(th.)}$, consistent within two standard deviations with the expected value. No evidence of a significant excess of events beyond the Standard Model is found and leptophobic $Z'$ bosons with democratic axial couplings to all quark generations are excluded in the probed mass range.